Although San Mateo County had issued an arrest warrant for Valencia as a suspect in the theft of the van in which Leuenberger's body was found, there was not enough evidence to charge him with homicide. Mexican citizens suspected of auto theft cannot be extradited from their country under treaty with the United States.

The two San Francisco Police homicide inspectors responsible for the coup - Spanish-speaking Antonio Casillas and veteran Tony Camilleri - declined to be interviewed for this story.

Their boss, Lt. David Robinson, refused to get into details of the case but said, "This wouldn't have happened without their tenacity and skill."

Based on interviews with law enforcement sources and Valencia's relatives in the United States and Mexico, the following account emerged:

Quick flight&lt;

Within 48 hours of finding Leuenberger's body, police learned that Valencia had fled the country.

With Valencia in Mexico, there was no way to attempt to match his DNA or fingerprints to evidence found at the crime scene.

However, through Valencia's family members in the Bay Area and in Los Angeles County, Casillas and Camilleri traced the wanted man back to the small village of San Juan Nuevo in the hilly northern region of the central Mexican state of Michoacan. In that town of 6,000, Valencia's relatives are well-known and highly respected. Both his grandfathers had served as mayor. The family is not wealthy, but it is well established.

Using his Spanish skills, Casillas began working the phones. He called Valencia's uncles in the Los Angeles area, asking them for cooperation. He then contacted Valencia's family in Mexico and prevailed on them to encourage the young man to return to the United States.

Close-knit Mexican family &lt;

The fact that Valencia came from a close-knit, well-known family in Mexico proved to be an advantage to police. The nature of the crime - and the possibility that a relative may be linked to it - left the family stunned. In a small town, word spread quickly.

"It was an appeal to their sense of dignity, their sense of life's value," Robinson said.

Valencia's relatives told The Examiner that the young man insisted he was innocent. They believed him but admitted they were troubled.

"He said he knew nothing about it," said Valencia's mother, Aurora Cuara. "He said he wasn't guilty."

Her sister, Esperanza Cuara, recalls telling him, "If you didn't do anything, you don't have anything to fear. Even if they lock you up, your conscience will be clear. But if you had something to do with it, you have to learn to accept your responsibility."

Many conversations with family &lt;

For several days last week, there were negotiations between Casillas and the family. Last Tuesday, Casillas spoke directly with Valencia for a long time.

The family agreed to go to Tijuana and let investigators speak to Valencia under the watchful eyes of Mexican police and prosecutors, according to Valencia's uncle, Arcacio Anguiano.

In Mexico, Casillas presented the case to them. Valencia denied any involvement in Leuenberger's kidnap and death. Then, despite warnings from Mexican police that he was abdicating his rights, Valencia agreed to come back to the United States.&lt;